Many cellular events and processes are characterized by altered expression levels of one or more genes. Differences in gene expression correlate with many physiological processes such as cell cycle progression, cell differentiation and cell death. Changes in gene expression patterns also correlate with changes in disease or pharmacological state. For example, the lack of sufficient expression of functional tumor suppressor genes and/or the over expression of oncogene/protooncogenes could lead to tumorgenesis (Marshall, Cell, 64: 313–326 (1991); Weinberg, Science, 254: 1138–1146 (1991), incorporated herein by reference in their entireties for all purposes). Thus, changes in the expression levels of particular genes (e.g. oncogenes or tumor suppressors) serve as signposts for different physiological, pharmacological and disease states.
Gene expression profiles produce a snapshot that reflects the biological status of the sample, but in many circumstances biological status will reflect more than one characteristic of the sample. For example, when comparing tumor samples from two patients, there will be changes that correlate with differences between the states of the tumors as well as changes that correlate with the different physiological states of the two patients. High-throughput technologies, such as DNA microarrays, have been used to profile and monitor gene expression of hematopoietic tumors (see Alizadeh et al., 2000; Golub et al., 1999 each incorporated by reference in their entireties for all purposes) and solid tumor homogenates and cell lines (see Alon et al., 1999, Perou et al., 2000, Sgroi et al., 1999 each incorporated by reference in their entireties for all purposes). However, the cell-specific profiling of solid tumor gene expression has been hampered by the inability to procure specific pure cell populations. A need exists to identify genes associated with normal and solid tumor cancerous cell conditions and to further correlate the expression levels of genes as a way of detecting or diagnosing a cancerous condition.